On the driver's side roll bar, right ahead of the sound bar. That's where they are with the factory Sirius option. Nothing metal above that point to block the signal.
Same with mine. I fabricated a bracket made of steel for the antenna to stick to (using the magnet on the antenna) and ran the antenna wire underneath the roll bar padding; it keeps the antenna from moving around that way. Quadratec sells something similar to what I made for about $25.
"Courage is being scared to death.....and saddling up anyway." - John Wayne